U.S. patent application number 15/725620 was filed with the patent office on 2018-02-01 for systems and methods for chemical vapor infiltration and densification of porous substrates.
This patent application is currently assigned to GOODRICH CORPORATION. The applicant listed for this patent is GOODRICH CORPORATION. Invention is credited to Tod POLICANDRIOTES.
Application Number | 20180030593 15/725620 |
Document ID | / |
Family ID | 61009331 |
Filed Date | 2018-02-01 |
United States Patent
Application |
20180030593 |
Kind Code |
A1 |
POLICANDRIOTES; Tod |
February 1, 2018 |
SYSTEMS AND METHODS FOR CHEMICAL VAPOR INFILTRATION AND
DENSIFICATION OF POROUS SUBSTRATES
Abstract
A system for chemical vapor infiltration and densification may
comprise a reaction chamber and a plurality of conduits fluidly
coupled to an exhaust outlet of the reaction chamber. A first set
of conduits of the plurality of conduits may define a first flow
path and a second set of conduits of the plurality of conduits may
define a second flow path. The second flow path may be fluidly
coupled to an inlet of the reaction chamber. A hydrogen extraction
component may be in fluid communication with a least one of the
first set of conduits or the second set of conduits.
Inventors: |
POLICANDRIOTES; Tod;
(Suffield, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GOODRICH CORPORATION |
CHARLOTTE |
NC |
US |
|
|
Assignee: |
GOODRICH CORPORATION
CHARLOTTE
NC
|
Family ID: |
61009331 |
Appl. No.: |
15/725620 |
Filed: |
October 5, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15078882 |
Mar 23, 2016 |
|
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15725620 |
|
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62137214 |
Mar 23, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 9/10 20130101; C23C
16/45593 20130101; F25B 9/12 20130101; C23C 16/045 20130101; C04B
35/83 20130101; C04B 2235/614 20130101; C23C 16/26 20130101; C23C
16/4412 20130101 |
International
Class: |
C23C 16/04 20060101
C23C016/04; F25B 9/12 20060101 F25B009/12; C04B 35/83 20060101
C04B035/83 |
Claims
1. A system for chemical vapor infiltration and densification, the
system comprising: a reaction chamber; a plurality of conduits
fluidly coupled to an exhaust outlet of the reaction chamber,
wherein a first set of conduits of the plurality of conduits define
a first flow path and a second set of conduits of the plurality of
conduits define a second flow path, wherein the second flow path is
fluidly coupled to an inlet of the reaction chamber; a roughing
pump fluidly coupled to the first set of conduits; a first valve in
operable communication with the first set of conduits; a second
valve in operable communication with the second set of conduits;
and a hydrogen extraction component in fluid communication with a
least one of the first set of conduits or the second set of
conduits, wherein the hydrogen extraction component comprises at
least one of a cryogenic-cooler or a pressure swing absorption
unit.
2. The system of claim 1, wherein the cryogenic-cooler is
configured to condense hydrocarbon molecules comprised of six or
more carbon atoms.
3. The system of claim 1, further comprising a first pump
downstream from the second valve, wherein the first pump comprises
at least one of a constant speed turbo pump, a variable speed turbo
pump, a constant speed dry pump, or a variable speed dry scroll
pump.
4. The system of claim 3, further comprising a second pump
downstream of the first pump, the second pump comprising at least
one of a diaphragm pump, a turbo pump, or a dry pump.
5. The system of claim 1, further comprising an electric arc
located proximate the exhaust outlet of the reaction chamber.
6. The system of claim 5, wherein the electric arc is configured to
breakdown hydrocarbon gases comprised of six or more carbon
atoms.
7. The system of claim 1, further comprising a stage disposed
within a reaction zone of the reaction chamber, wherein the stage
is electrically isolated from a wall of the reaction chamber.
8. The system of claim 1, wherein the cryogenic-cooler comprises at
least one of a helium cryogenic cooler or a liquid nitrogen
condenser.
9. A method of chemical vapor infiltration and deposition,
comprising: disposing a porous substrate within a reaction chamber;
establishing a sub-atmospheric pressure within the reaction
chamber; introducing a hydrocarbon reaction gas into a reaction
zone of the reaction chamber to densify the porous substrate;
withdrawing unreacted hydrocarbon reaction gas from the reaction
chamber, the unreacted hydrocarbon reaction gas comprising
hydrocarbon molecules having six or more carbon atoms; removing at
least a portion of the hydrocarbon molecules having six or more
carbon molecules from the unreacted hydrocarbon reaction gas by
causing the portion of the hydrocarbon molecules having six or more
carbon atoms to condense; and recirculating at least a portion of
the unreacted hydrocarbon reaction gas back into the reaction
zone.
10. The method of claim 9, further comprising applying an
electrical voltage to the porous substrate.
11. The method of claim 9, wherein removing the portion of the
hydrocarbon molecules having six or more carbon molecules from the
unreacted hydrocarbon reaction gas comprises flowing the unreacted
hydrocarbon reaction gas through a trap including one or more sets
of rotating blades.
12. The method of claim 9, further comprising extracting hydrogen
from the unreacted hydrocarbon reaction gas.
13. The method of claim 12, wherein the extracting hydrogen
comprises flowing the unreacted hydrocarbon reaction gas through at
least one of a cryogenic-cooler or a pressure swing absorption
unit.
14. The method of claim 9, further comprising applying an electric
arc to the unreacted hydrocarbon reaction gas withdrawn from the
reaction chamber.
15. The method according of claim 9, further comprising heating at
least one of the hydrocarbon reaction gas or the portion of the
unreacted hydrocarbon reaction gas recirculated into the reaction
zone using a charged coil located proximate an inlet of the
reaction chamber, wherein the charged coil provides an electrical
conduction path to at least one of charge or ground an interior
wall of the reaction chamber.
16. A system for chemical vapor infiltration and densification, the
system comprising: a reaction chamber; a plurality of conduits
fluidly coupled to an exhaust outlet of the reaction chamber,
wherein a first set of conduits of the plurality of conduits define
a first flow path and a second set of conduits of the plurality of
conduits define a second flow path, wherein the second flow path is
fluidly coupled to an inlet of the reaction chamber; and a hydrogen
extraction component in fluid communication to a least one of the
first set of conduits or the second set of conduits, wherein the
hydrogen extraction component comprises at least one of a
cryogenic-cooler or a pressure swing absorption unit.
17. The system of claim 16, wherein the at least one of the
cryogenic-cooler or the pressure swing absorption unit is
configured to condense hydrocarbon molecules comprised of six or
more carbon atoms.
18. The system of claim 16, further comprising an electric arc
located proximate the exhaust outlet of the reaction chamber.
19. The system of claim 16, further comprising a trap in fluid
communication with at least one of the first set of conduits or the
second set of conduits, the trap including one or more sets of
rotating blades configured to breakdown hydrocarbon molecules
having six or more carbon atoms.
20. The system of claim 19, further comprising a plasma conduit
located upstream from the trap, wherein the plasma conduit is
configured to breakdown a first hydrocarbon molecule having six or
more carbon atoms into a plurality of second hydrocarbon molecules
each having less than six carbon atoms.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of, claims
priority to and the benefit of, U.S. Ser. No. 15/078,882, filed
Mar. 23, 2016 and entitled "METHOD FOR RAPID AND EFFICIENT CHEMICAL
VAPOR INFILTRATION AND DENSIFICATION OF CARBON FIBER PREFORMS,
POROUS SUBSTRATES AND CLOSE PACKED PARTICULATES." The '882
application claims priority to and the benefit of U.S. Provisional
Application No. 62/137,214 filed Mar. 23, 2015 and entitled "METHOD
FOR RAPID AND EFFICIENT CHEMICAL VAPOR INFILTRATION AND
DENSIFICATION OF CARBON FIBER PREFORMS, POROUS SUBSTRATES AND CLOSE
PACKED PARTICULATES." All the aforementioned applications which are
hereby incorporated by reference in their entirety for all
purposes.
FIELD
[0002] The present disclosure relates to chemical vapor
infiltration and densification, and more specifically, to systems
and methods of chemical vapor infiltration and densification
employing recirculated hydrocarbon gases.
BACKGROUND
[0003] Carbon fiber/carbon matrix (C/C) composites are used in the
aerospace industry for aircraft brake heat sink materials, among
other applications. Silicon carbide (SiC) based ceramic matrix
composites (CMCs) have found use as brake materials and other
components in automotive and locomotive industries. These
composites may be typically produced using, for example, chemical
vapor infiltration (CVI) or chemical vapor deposition (CVD). Such
processes generally include placing porous preforms into a reactor
and introducing a gaseous precursor to form silicon carbide
depositions within the pores of the preform. The SiC may be
deposited as a coating or series of coatings wherein a porous
sample or preform may be densified with carbon then SiC, or with
SiC then carbon.
[0004] However, conventional infiltration and/or or deposition
processes tend to result in byproduct deposits accumulating within
system components of the manufacturing system, such as the exhaust
piping. The byproduct deposits may be reactive and even pyrophoric,
and thus precautions are warranted to promote a safe manufacturing
environment. For example, conventional manufacturing systems are
often shut-down for periods of time while users manually clean the
components and piping of the manufacturing system to remove the
byproduct deposits. This cleaning procedure increases the downtime
of the manufacturing system and thus decreases the capacity and
throughput of conventional ceramic matrix composite manufacturing
systems. Buildup of condensable hydrocarbon tars from conventional
carbon CVI processes, although not pyrophoric in nature tends to
cause reductions in throughput of the plumbing systems (similar to
deposits of cholesterol in a person's arteries).
SUMMARY
[0005] A system for chemical vapor infiltration and densification
is disclosed, in accordance with various embodiments. The system
may comprise a reaction chamber and a plurality of conduits fluidly
coupled to an exhaust outlet of the reaction chamber. A first set
of conduits of the plurality of conduits may define a first flow
path and a second set of conduits of the plurality of conduits may
define a second flow path. The second flow path may be fluidly
coupled to an inlet of the reaction chamber. A roughing pump may be
fluidly coupled to the first set of conduits, A first valve may be
in operable communication with the first set of conduits. A second
valve may be in operable communication with the second set of
conduits. A hydrogen extraction component may be in fluid
communication with a least one of the first set of conduits or the
second set of conduits. The hydrogen extraction component may
comprise at least one of a cryogenic-cooler or a pressure swing
absorption unit.
[0006] In various embodiments, the cryogenic-cooler may be
configured to condense hydrocarbon molecules comprised of six or
more carbon atoms. A first pump may be downstream from the second
valve. The first pump may comprise a constant speed turbo pump, a
variable speed turbo pump, a constant speed dry pump, or a variable
speed dry scroll pump. A second pump may be downstream of the first
pump. The second pump may comprise at least one of a diaphragm
pump, a turbo pump, or a dry pump.
[0007] In various embodiments, an electric arc may be located
proximate the exhaust outlet of the reaction chamber. The electric
arc may be configured to breakdown hydrocarbon gases comprised of
six or more carbon atoms. A stage may be disposed within a reaction
zone of the reaction chamber. The stage may be electrically
isolated from a wall of the reaction chamber. The cryogenic-cooler
may comprise at least one of a helium cryogenic cooler or a liquid
nitrogen condenser.
[0008] A method of chemical vapor infiltration and deposition is
disclosed, in accordance with various embodiments. The method may
comprise disposing a porous substrate within a reaction chamber,
establishing a sub-atmospheric pressure within the reaction
chamber, introducing a hydrocarbon reaction gas into a reaction
zone of the reaction chamber to densify the porous substrate, and
withdrawing unreacted hydrocarbon reaction gas from the reaction
chamber. The unreacted hydrocarbon reaction may comprise
hydrocarbon molecules having six or more carbon atoms. The method
may further comprise removing at least a portion of the hydrocarbon
molecules having six or more carbon molecules from the unreacted
hydrocarbon reaction gas by causing at least a portion of the
hydrocarbon molecules having six or more carbon atoms to condense,
and recirculating at least a portion of the unreacted hydrocarbon
reaction gas back into the reaction zone.
[0009] In various embodiments, the method may further comprise
applying an electrical voltage to the porous substrate. In various
embodiments, removing the portion of the hydrocarbon molecules
having six or more carbon molecules from the unreacted hydrocarbon
reaction may comprise flowing the unreacted hydrocarbon reaction
gas through a trap including one or more sets of rotating
blades.
[0010] In various embodiments, the method may further comprise
extracting hydrogen from the unreacted hydrocarbon reaction gas. In
various embodiments, extracting hydrogen may comprise flowing the
unreacted hydrocarbon reaction gas through at least one of a
cryogenic-cooler or a pressure swing absorption unit. The method
may further comprise applying an electric arc to the unreacted
hydrocarbon reaction gas withdrawn from the reaction chamber. The
method may further comprise heating at least one of the hydrocarbon
reaction gas or the portion of the unreacted hydrocarbon reaction
gas recirculated into the reaction zone using a charged coil
located proximate an inlet of the reaction chamber. The charged
coil may provide an electrical conduction path to at least one of
charge or ground an interior wall of the reaction chamber.
[0011] A system for chemical vapor infiltration and densification
is disclosed, in accordance with various embodiments. The system
may comprise a reaction chamber and a plurality of conduits fluidly
coupled to an exhaust outlet of the reaction chamber. A first set
of conduits of the plurality of conduits may define a first flow
path and a second set of conduits of the plurality of conduits may
define a second flow path. The second flow path may be fluidly
coupled to an inlet of the reaction chamber. A hydrogen extraction
component may be in fluid communication with a least one of the
first set of conduits or the second set of conduits. The hydrogen
extraction component may comprise at least one of a
cryogenic-cooler or a pressure swing absorption unit.
[0012] In various embodiments, the cryogenic-cooler or the pressure
swing absorption unit may be configured to condense hydrocarbon
molecules comprised of six or more carbon atoms. An electric arc
may be located proximate the exhaust outlet of the reaction
chamber. A trap may be in fluid communication with at least one of
the first set of conduits or the second set of conduits. The trap
may include one or more sets of rotating blades configured to trap
and condense hydrocarbon molecules having six or more carbon atoms.
A plasma conduit may be located upstream from the trap. The plasma
conduit may be configured to breakdown a first hydrocarbon molecule
having six or more carbon atoms into a plurality of second
hydrocarbon molecules each having less than six carbon atoms.
[0013] The foregoing features and elements may be combined in
various combinations without exclusivity, unless expressly
indicated otherwise. These features and elements as well as the
operation thereof will become more apparent in light of the
following description and the accompanying drawings. It should be
understood, however, the following description and drawings are
intended to be exemplary in nature and non-limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a schematic diagram of a system for
chemical vapor infiltration and densification comprising a
recirculation path, in accordance with various embodiments;
[0015] FIG. 2 illustrates a schematic diagram of a system for
chemical vapor infiltration and densification comprising a
recirculation path, in accordance with various embodiments;
[0016] FIG. 3 illustrates a schematic diagram of a system for
chemical vapor infiltration and densification comprising a
recirculation path and cryogenic cooling stage, in accordance with
various embodiments;
[0017] FIG. 4 is a graph comparing densification of porous
structures in CVI/CVD systems employing recirculated effluent gas
to densification of porous structures in CVI/CVD systems employing
an increased virgin reaction gas flow rate, in accordance with
various embodiments;
[0018] FIGS. 5A and 5B illustrate a method of chemical vapor
infiltration and deposition;
[0019] FIG. 6A illustrates a retort having a frustoconical retort
lid, in accordance with various embodiments; and
[0020] FIG. 6B illustrates a frustoconical retort lid, in
accordance with various embodiments.
[0021] The subject matter of the present disclosure is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. A more complete understanding of the present
disclosure, however, may best be obtained by referring to the
detailed description and claims when considered in connection with
the drawing figures, wherein like numerals denote like
elements.
DETAILED DESCRIPTION
[0022] The detailed description of exemplary embodiments herein
makes reference to the accompanying drawings, which show exemplary
embodiments by way of illustration. While these exemplary
embodiments are described in sufficient detail to enable those
skilled in the art to practice the exemplary embodiments of the
disclosure, it should be understood that other embodiments may be
realized and that logical changes and adaptations in design and
construction may be made in accordance with this disclosure and the
teachings herein. Thus, the detailed description herein is
presented for purposes of illustration only and not limitation. The
steps recited in any of the method or process descriptions may be
executed in any order and are not necessarily limited to the order
presented. Furthermore, any reference to singular includes plural
embodiments, and any reference to more than one component or step
may include a singular embodiment or step. Also, any reference to
attached, fixed, connected or the like may include permanent,
removable, temporary, partial, full and/or any other possible
attachment option. Additionally, any reference to without contact
(or similar phrases) may also include reduced contact or minimal
contact.
[0023] Throughout the present disclosure, like reference numbers
denote like elements. Accordingly, elements with like element
numbering may be shown in the figures, but may not be necessarily
be repeated herein for the sake of clarity.
[0024] Provided herein, according to various embodiments, are
manufacturing systems and associated methods for fabricating C/C
composite components. The systems and associated methods may
provide for rapid and efficient deposition of carbon on and within
carbon fiber preforms, porous substrates, and/or close packed
particulates by pyrolytic carbon in the structures of isotropic,
anisotropic, graphitic, amorphous, lonsdaleite, and diamond. The
preforms, porous substrates, and/or close packed particulates are
placed into a vacuum-tight reaction chamber as a shape, form, or
mold and may be electrically isolated from the surrounding system.
The reaction chamber may include a reaction zone defined by a
retort within the reaction chamber. After loading the samples
(i.e., the carbon fiber preforms, porous substrates, and/or close
packed particulates) in the reaction zone, the reaction chamber may
be evacuated to remove atmospheric gases. The samples can be
grounded, charged with a positive or negative direct current (DC)
voltage, or frequency oscillated using an alternating current (AC)
voltage (that can be biased positively or negatively) independent
of the whole system. The interior walls of the retort may be either
grounded or electrically isolated from the surrounding system and
the sample. The retort may be brought to an isothermal or gradient
temperature condition above room temperature in a vacuum, with or
without an inert gas. Once the set point temperature and pressure
are achieved and controlled, one or more dry
recycling/recirculating pumps may be activated in a circuit
extending between the reaction chamber's exhaust to the reaction
chamber's inlet/input. One or more hydrocarbon (CxHy) reaction
gases, and/or inert carrier gases, and/or hydrogen gas are input
into the vacuum tight reaction chamber/retort, either as a mixture
or independently. The hydrocarbon reaction gases, and/or inert
carrier gases, and/or hydrogen gas may be brought up to the
reaction chamber temperature through a series of tubing coils.
[0025] The system may be under constant recycling/recirculating
through the duration of the densification process by constant or
variable speed dry pumps. One or more valve(s), in fluid
communication with the pumps, may be configured to control a
recycling/recirculating of effluent gas exhausted from the reaction
zone. Translation (e.g., opening or closing) of the valves may
pulsate the system and/or cause a cessation of the
recycling/recirculating of the effluent gases. The internal system
vacuum pressure may be controlled by one or more mass flow/pressure
controllers and/or throttle valves located upstream and downstream
of the reaction zone. On the exhaust side (downstream side) of the
reaction zone, where the exhaust temperature begins to reduce just
before the heavy hydrocarbons condense, variable or constant plasma
may be created, using an electric arc method, such that the remnant
hydrocarbon gases (i.e., the effluent hydrocarbon gases exiting the
reaction zone) cross through the plasma when exiting the reaction
zone, thereby reducing the heavier hydrocarbons (e.g., hydrocarbons
molecules comprised of six or more carbon atoms) to simpler
hydrocarbons (e.g., hydrocarbons molecules comprised of five or
less carbon atoms). Depending on the particular gas or gas mixture
input, additional plasma reactions may be performed near the
reaction zone's exhaust point to further reduce the heavy
hydrocarbons to simpler hydrocarbons.
[0026] At various points in the system plumbing, the downstream
exhaust gas (also referred to herein as effluent gas) may be
monitored to ascertain the type and/or concentration of hydrocarbon
molecules within the exhaust gas. The system may comprise one more
valves which may fine tune the process (e.g., adjust the volume,
speed, hydrocarbon molecule size, or other feature(s) of the
exhaust gas being recycled) to minimize the hydrocarbon gases
exiting the system completely. During the process, a mass of the
sample(s) (i.e., a mass of the preforms, porous substrates, and/or
close packed particulates) may be measured continuously using an
in-situ measurement device such as a precision load cell.
[0027] A chemical vapor infiltration system 100 for rapidly and
efficiently densifying carbon fiber preforms, porous substrates,
and close packed particulates by pyrolytic carbon in the structure
of one or more of isotropic, anisotropic, graphitic, amorphous,
lonsdaleite, and diamond and mixtures of said structures, is shown
schematically in FIG. 1, in accordance with various
embodiments.
[0028] The parts of the system shown in FIG. 1 include:
[0029] 1. roughing pump
[0030] 2. turbo pump
[0031] 3. 3 way valve
[0032] 4. throttle valve
[0033] 5. sampling port/valve
[0034] 6. valves
[0035] 7, 8, 9. Turbo pumps and/or scroll pumps
[0036] 10. flow controller
[0037] 11. pressure measurement
[0038] 12. valve
[0039] 13. optional diaphragm pump/plasma chamber
[0040] 14. sampling port
[0041] 15. gas inlet tube
[0042] 16. sample stage
[0043] 17. pressure measurement
[0044] 18. high voltage input for plasma
[0045] 19. retort
[0046] 20. plasma conduit
[0047] 21. gas feed
[0048] 22. load cell/rotary, motor
[0049] 23. element power feedthrough
[0050] 24. voltage input for plasma conduits (optional for high
efficiency)
[0051] 25. inert gas input
[0052] 26. valve
[0053] 27. inert gas for power feeds
[0054] 28. gas sampling port
[0055] 29. insulated water cooled chamber with enclosed element and
electrically non-conductive retort
[0056] 30. reaction zone
[0057] 31. retort lid/Venturi cone
[0058] 35. bleed line
[0059] 36. one way flow valve
[0060] 38. pressure swing absorption unit
[0061] 39. mass flow control
[0062] 40. virgin gas source
[0063] 41. conduit
[0064] 62. outlet of reaction zone.
[0065] System 100 may comprise a fluid cooled reaction chamber 29.
The chamber 29 may be generally cylindrical. In various
embodiments, the chamber 29 has an internal diameter of 10.0 inches
(25.4 cm), and a height of 16.0 inches (40.6 cm). However, the
chamber 29 can be scaled up or down, and the sizes of the other
components, such as the power supplies, scaled accordingly. The gas
flow rates may also be adjusted to optimize the recirculation and
densification process. System 100 may be controlled by engineering
software. For example, a suitable systems engineering software may
control the system and collect data in real time, and is available
from National Instruments, 11500 Mopac Expressway, Austin, Tex.
(U.S.A.) under the tradename Labview.RTM..
[0066] In various embodiments, a sample may be loaded onto an
electrically isolated sample stage/support 16 inside a reaction
zone 30 defined by a retort 19 located within the chamber 29.
Stated differently, reaction zone 30 may be located within retort
19. In various embodiments, chamber 29 may comprise a vacuum tight
oven/furnace. In various embodiments, stage 16 may comprise an
in-situ electrically isolated sample balance.
[0067] Referring to FIGS. 6A and 6B, retort 19 may comprise a
retort lid 31 coupled to a generally cylindrical retort body 33.
Retort lid 31 may be located proximate an outlet 62 of reaction
zone 30. Retort lid 31 may be configured to have a Venturi effect
at the outlet 62 of reaction zone 30. In various embodiments,
retort lid 31 may comprise a Venturi cone. Stated differently,
retort lid 31 may comprise a generally frustoconical shape.
[0068] Atmospheric gases may be evacuated with a roughing vacuum
pump 1 and/or turbo vacuum pump 2 to a pressure below 2 Torr (266.6
pascal (Pa)). Inert gas may be input into reaction zone 30 to force
out any remaining atmospheric gases in the reaction zone 30 and/or
chamber 29. The chamber 29 is heated to the desired temperature set
point with a heater, and the pressure is maintain below 100 Torr
(13,332.2 Pa). Inert gas may be provided to the chamber 29 through
the power feedthroughs 23/25 at flows less than or equal to 150
standard cubic centimeter per minute (sccm or cm.sup.3/min) (i.e.,
less than or equal to 9.15 in.sup.3/min) at the location of the
stage 16. When the set point temperature (isothermal or gradient),
is reached, one or more dry recycling/recirculating pumps 7, 8, 9,
and/or 13 may be turned on. Pumps 7, 8, 9, and 13 may comprise one
or more constant or variable speed turbo pumps, constant or
variable speed dry pumps, diaphragm pumps, or other suitable pump
and/or combinations thereof.
[0069] The exhaust to inlet circuit is opened and the flow and
make-up of the recirculated gas can be measured and analyzed at a
point (e.g., at sampling port 14) before the recirculated gases are
input into reaction zone 30. For example, the recirculated gas may
be analyzed proximate to a low pressure one way flow valve 36
located just prior to (i.e., upstream from) the point where the
recirculated gas and virgin gas are combined and input into
reaction chamber 29. As used herein, "virgin gas" refers to gas
that has not yet flowed through reaction zone 30. As used herein,
"recirculated gas" refers to gas that has flowed through reaction
zone 30 at least one time. In various embodiments, prior to being
input into reaction zone 30, the virgin gas and the recirculated
gas may be combined in a single conduit (e.g., gas inlet tube 15).
In various embodiments, the virgin gas and the recirculated gas may
be input into reaction zone 30 via separate conduits. Stated
differently, a first conduit may be coupled between virgin gas
source 40 and reaction zone 30, and a second conduit, discrete from
the first conduit, may be coupled between one way flow valve 36 and
reaction zone 30. In various embodiments, a mass flow control (MFC)
39 may be in operable communication with virgin gas source 40 and
may measure and control a flow rate of virgin reaction gas input
into reaction zone 30. In various embodiments, the flow of virgin
gas may be adjusted in response to data obtained at sampling port
14.
[0070] The vacuum pressure may be set to a desired level and
exhausted through a flow controller such as a throttle valve 4 at a
point immediately after the first recycle/recirculating turbo pump
7 connected by conduits and separated by a valve 26 that can be
opened or closed at any time for the process. The diameter/orifice
size of the conduits and valves may be varied throughout system 100
to control flow output to the throttle valve 4. The output may pass
through a secondary turbo pump 2 just prior to the roughing vacuum
pump 1. Virgin hydrocarbon reaction gases such as for example,
methane 0-100 liter per minute (L/min) (0-26.4 gal/min), propane
0-50 L/min (0-13.2 gal/min), natural gas mixtures 0-150 L/min
(0-39.6 gal/min), or any desired hydrocarbon reaction gas can be
introduced right after the one way flow valve 36 on the
inlet/upstream side of reaction zone 30. Hydrogen can be included
or excluded from the process depending on the microstructure
desired. For example, a pressure swing absorption swing (PSA) 38 or
magnetite filter may be located upstream of one way How valve 36,
and may extract hydrogen from the recirculated gas. The pressure
within system 100 may be maintained below 100 Torr (13,332.2 Pa),
either at a constant pressure or pulsed from a low pressure to a
higher pressure 100 Torr or less (13,332.2 Pa or less)
[0071] The sample(s), which may be located on stage 16, can either
be grounded or charged by a constant positive or negative DC
voltage or an AC voltage that can be frequency varied and/or
positively/negatively biased. The walls of the retort 19 can be
grounded, or positively or negatively charged, but are isolated
from the sample(s). In various embodiments, the sample may be
negatively charged, and the walls of the retort 19 may be
configured to be insulating. The contact between the reaction gases
and the heating elements may be minimized. The Venturi effect may
be utilized at the exhaust side of the chamber 29/retort 19 (i.e.,
at lid 31) to separate the phases of the reaction gas. The Venturi
effect may also be utilized at the first recirculating turbo pump
7. At a point on the exhaust side of reaction zone 30 (i.e., after
outlet 62) and before the first recycle/recirculating pump 7, a
bleed line 35 may be fed to a precision flow controller 10 (e.g., a
throttle valve), which bypasses the throttle valve 4, and to the
primary exhaust turbo pump 2 before the roughing pump 1. In this
regard, a portion of the gas downstream of valve 26 may be directed
through bleed line 35 to roughing pump 1. Bleed line 35 may also
fluidly coupled to a point after (i.e., downstream from) the
recycle/recirculating pumps 7, 8, 9. In this regard, a portion of
the gas downstream from pump 9 may be directed through bleed line
35 to roughing pump 1. When the main throttle valve 4 is closed,
the precision flow controller 10 may be engaged to control the
pressure within system 100. In various embodiments, the conduits of
bleed line 35 may have a diameter that is equal to or less than
1/4th the diameter of the main recirculating path plumbing (i.e.,
conduits). The exhaust gas can be analyzed (e.g., at sampling port
28) and the recirculating flow rate adjusted to increase the
process efficiency. For example, in response to the data output
from sampling port 28, a larger or a smaller portion of the
recirculated gas may be directed through bleed line 35 and roughing
pump 1 to maintain a desired pressure and/or recirculation flow
rate within system 100. Because the system is continuously
recycled/recirculated, the main upstream flow inlet can be shut off
simultaneously with the exhaust and recirculated to extract most of
the carbon in the hydrocarbon gases.
[0072] During the process described above, an electric arc variable
frequency or fixed de corona plasma 20 can be implemented at the
Venturi point (i.e., the retort lid 31) at the outlet 62 of
reaction zone 30, near where the exhausting gas begins to condense
out the heavy hydrocarbons as tars in order to breakdown and form
simpler hydrocarbon reaction gases for the purpose of
recycling/recirculating back into reaction zone 30. Additional
electric arc corona plasmas can be used prior to the bleed line 35
before the first recycling/recirculating pump 7. To extract excess
hydrogen on the exhaust side a magnetite filter can be used after
the plasma treatment. In addition, the entire recirculating
plumbing, before and after (upstream of and downstream of) the
turbines of pumps 7, 8, 9, can be high temperature plasma transfer
lines. The recirculating plumbing may be designed to incorporate a
solenoidal electromagnet system surrounding the plasma tubing
thereby enhancing the partially/fully ionized plasma and allowing
for further adjustment of stream density and direction.
[0073] Pumps 7, 8, 9, may comprise a controllable variable speed
turbo/turbine vacuum pump with either an in-line or 90 degree exit
port that can operate at vacuum pressures above 3 Torr (400.0 Pa)
with the turbine blades made from stainless steel, CMC or other
high strength, high temperature alloys or composites. The entrance
and/or exit ports of the pumps 7, 8, 9 may utilize the Venturi
effect to enhance gas flow. The pumps 7, 8, 9 can be air powered,
electric motor powered, fluid powered, etc. with or without
magnetic bearings. The higher the rpm the better as far as flow
capability. Though there may be no upper limit, a lower limit of
10,000 rpm may be reasonable for the system.
[0074] Pumps 7, 8, 9, may comprise one or more constant or variable
speed inline turbo pump(s) or 90 degree turbo pump(s), or one or
more constant or variable speed dry pump(s). Pumps 7, 8, 9 may be
used to recycle/recirculate the reaction gases not consumed in the
first pass through the reaction zone 30 (i.e., the gases output at
outlet 62). In various embodiments, system 100 may employ pumps 7,
8, 9 without plasma circulation.
[0075] In various embodiments, partially or fully ionized
hydrocarbon, argon, helium, hydrogen or combinations and mixtures
of gases including a hydrocarbon gas, may use plasma conduits to
flow and recirculate said gases with or without the use of one or
more the pumps 7, 8, 9 to aid in the recirculation.
[0076] A dry diaphragm pump 13 can be used either alone or in
combination with one or more of the pump(s) 7, 8, 9 to
recycle/recirculate the hydrocarbon gases in the CVI/CVD process to
improve efficiency and the rate of carbon deposition (i.e. preform
densification).
[0077] In various embodiments, hydrocarbon gases, including heavy
hydrocarbons, are recycled/recirculated and/or modified to improve
the rate of densification and the efficiency of the CVI/CVD
process.
[0078] In various embodiments, an electric arc corona plasma may be
used to breakdown heavy hydrocarbon gases by either constant or
variable DC voltages and/or constant or variable frequency AC
voltages that can be biased negatively or positively. For increased
efficiency, the plasma may be contained within the complete
recirculation circuit such that the recirculated gases are
dissociated and kept at a high temperature.
[0079] The sample(s) to be densified may be electrically isolated
from the system and either grounded or negatively or positively
charged with DC voltage or by an AC voltage which can be frequency
modulated and biased positively or negatively to increase the rate
of deposition and the efficiency.
[0080] The retort 19 may be electrically isolated from the
sample(s). The retort may be grounded, or charged with DC or AC
voltages.
[0081] A turbo vacuum pump 7 can be followed by a dry diaphragm
pump 13 or multiple turbo pumps 8, 9 to aid in building up a
pressure higher than the reaction chamber 29 pressure at the
reaction gas entrance point to open an alternative one way flow
valve 36 directed toward the reaction chamber/retort to facilitate
continuous or pulsed recirculation.
[0082] The efficiency of the CVI/CVD process in depositing carbon
may be greater than 5% as measured by the total mass of carbon
contained in the total volume of the hydrocarbon gases used when
compared to the mass gain of the preform, substrate or particulate
mold. The sample(s) may be weighed using an in-situ measurement
process and device in the CVI/CVD system.
[0083] An electrically isolated coiled tube in or near the
electrically isolated retort 19 can be provided to preheat the
incoming reaction gases and provide an electrical conduction path
to charge or ground the interior walls of the electrically isolated
retort.
[0084] The Venturi effect can be used to separate the phases of the
hydrocarbon gases exiting the retort 19 for increasing efficiency
using a plasma at the point prior to or at the heavy hydrocarbon
condensation point within the reaction chamber exit tube.
[0085] In various embodiments, the recirculating/recycling may
occur after the roughing vacuum pump 1, which may be a dry vacuum
pump or a liquid vacuum pump. For example, in various embodiments,
at least a portion of the effluent gas exiting roughing pump 1 may
be recirculated into reaction zone 30 via a conduit 41. In various
embodiments, after the roughing pump 1, the effluent gas may go
through a pressure swing unit 38 or magnetite filter to extract
hydrogen before circulating back into the reaction zone 30.
[0086] In system 100, the effluent gases output from reaction
chamber 29 (also referred to herein as unreacted hydrocarbon gas),
at a pressure below atmospheric (e.g., less than 760 Torr (i.e.
less than 101,325.0 Pa)), are recirculated in a semi-closed loop.
In various embodiments, the effluent gases may be recirculated
through a condensing/plasma/"whipper" system configured to remove
condensable hydrocarbons of C6 variation or larger (i.e.,
hydrocarbons comprising six or more carbon atoms). In various
embodiments, the effluent gases may be recirculated through a
condensing/plasma/"whipper" system configured to remove condensable
hydrocarbons of C5 variation or larger (i.e., hydrocarbons
comprising five or more carbon atoms). The recirculated effluent
gases may then be input into the reaction zone 30. System 100
comprising a semi-closed loop allows the effluent gases to remain
within the system plumbing such that a pressure throughout the
system 100 remains fairly constant (e.g., the pressure remains
under 100 Torr (13,332.2 Pa)). The closed system may allow for
increased efficacy and lower energy costs as compared to
conventional recirculation systems, wherein the effluent gases are
removed from the system plumbing, filtered, and re-pressurized in
an external tank before being added back into the higher pressure
input stream. In system 100, the recirculated effluent gases may
increase the number of moles of small carbon molecules flowing
through reaction zone 30 and available for deposition within the
porous substrate, without increasing the flow and/or amount of
initial (i.e., virgin) reaction gas input into the system. Stated
differently, recirculating the effluent gases may increase the
densification rate, as more molecules are passing through the
reaction zone, which increases the number of molecules that will
make collisions (i.e., bond) with the porous substrate.
Accordingly, the disclosed CVI/CVD systems and methods may allow
for faster densification of carbon fiber preforms and/or
densification to greater than 1.7 g/cc. The disclosed systems and
methods of may further alleviate a need to machine the substrate to
reopen closed surface pores during densification. In this regard,
the substrate densification may be completed in a single CVI/CVD
cycle.
[0087] With reference to FIG. 2, a system 200 for chemical vapor
infiltration and densification is illustrated, in accordance with
various embodiments. System 200 may comprise a reaction chamber
129. Reaction chamber 129 may comprise a retort 119 defining an
internal reaction zone 130. Stated differently, reaction zone 130
is located in the interior of retort 119.
[0088] Retort 119 may be similar to retort 19 in FIG. 6A. Retort
119 may comprise a retort lid 131, similar to retort lid 31 in FIG.
6B. Retort lid 131 may be configured to have a Venturi effect. In
various embodiments, retort lid 131 may comprise a Venturi cone.
Stated differently, retort lid 131 may comprise a generally
frustoconical shape. Retort lid 131 may be located proximate an
outlet 162 of reaction zone 130.
[0089] A stage 116 is located within reaction zone 130. Stage 116
may be electrically isolated from various other components of
system 200 (e.g., from the heating elements 153 and or walls of
retort 119). During CVI/CVD, porous preform(s) 132 may be disposed
on stage 116. The porous preform(s) 132 may be grounded, charged
with a positive or negative DC voltage, or frequency oscillated
using an AC voltage that can be biased positively or
negatively.
[0090] A virgin gas source 140 may be fluidly coupled an inlet 152
of reaction chamber 129 via a conduit 142. As used herein, "virgin
gas" refers to gas that has not yet been sent through the reaction
zone 130. Virgin gas source 140 may supply methane, ethane,
propane, butane, natural gas mixtures, or any desired hydrocarbon
reaction gas to reaction zone 130. An MFC 146 may be in operable
communication with virgin gas source 140 and may measure and
control a flow rate of virgin reaction gas input into reaction zone
130. For example, MFC 146 may cause virgin gas source 140 to output
between 0-50 liter standard per minute (L/min) of virgin reaction
gas into reaction zone 130. In various embodiments, MFC 146 may
cause virgin gas source 140 to output between 0-100 liters/min
(L/min) of virgin reaction gas into reaction zone 130. In various
embodiments, MFC 146 may cause virgin gas source 140 to output
between 0-150 L/min (0-39.6 gal/min) of virgin reaction gas into
reaction zone 130. System 200 may comprise a load cell 148
configured to measure a mass of porous substrate 132 at various
points, or continuously, throughout the CVI/CVD process. MFC 146
may adjust the flow of virgin gas input into reaction zone 130, in
response to data output from one or more pressure or other type
sensors 192 located within system 200. In various embodiments, a
pressure within system 200 is maintained at or below 100 Torr
(13,332.2 Pa).
[0091] One or more inert gas inlets 154 may be in fluidly coupled
to reaction zone 130. Inert gas (e.g., argon and nitrogen) may be
input into reaction zone 130 to force atmospheric gases from
reaction zone 130. One or more heating elements 153 may be employed
to heat reaction zone 130 to a desired temperature (isothermal or
gradient).
[0092] A pre-heat zone 150 may be located between reaction zone 130
and inlet 152 of reaction chamber 129. Inlet 152 may comprise an
inlet for inputting the virgin reaction gases and the recirculated
gases, as discussed in further detail below, into reaction chamber
129. Pre-heat zone 150 may comprise heated and/or charged coils 151
configured to increase a temperature of the reaction gases (e.g.,
the virgin recirculated gases) entering reaction zone 130. In
various embodiments, coils 151 provide an electrical conduction
path to charge or ground an interior wall of retort 119. In various
embodiments, a high voltage and inert gas feedthrough 193 may be
located proximate inlet 152.
[0093] One or more conduits 163 may fluidly couple a roughing pump
160 an exhaust outlet 162 located at retort lid 131. In that
regard, effluent gases 164 may be drawn out of reaction zone 130 by
roughing pump 160. The effluent gases 164 may exit reaction zone
130 via outlet 162.
[0094] Upon exiting outlet 162, effluent gases 164 may be directed
through conduits 163. In various embodiments, conduits 163 may
diverge at an intersect point 165 such that a first set of conduits
163a define, at least a portion of, a first fluid path 177, and a
second set of conduits 163b define, at least a portion of, a second
fluid path 179. In that regard, effluent gases 164 may flow along
fluid path 177 (also referred to herein as an "exit path"),
represented by arrows 168, toward roughing pump 160 and/or effluent
gases 164 may flow along a fluid path 179 (also referred to herein
as a "recirculation path"), indicated by arrows 174, toward inlet
152. In various embodiments, at least a portion of the effluent gas
164 entering recirculation path 179 may be recirculated back into
reaction zone 130 via conduits 163b. A first valve 172 may be
located between roughing pump 160 and the intersect point 165. In
various embodiments, a turbo pump 173 may be located between the
first valve 172 and the roughing pump 160. In various embodiments,
a throttle valve 176 may located downstream of the first valve 172.
Stated differently, effluent gases 164 flow through throttle valve
176 after flowing though first valve 172. The vacuum pressure
within reaction zone 130 and throughout system 200 may be
maintained at a desired level by opening and closing throttle valve
176 and first valve 172 and/or by increasing and decreasing the
speed of roughing pump 160 and turbo pump 173.
[0095] A pump 180 may be located along the recirculation path 179.
Pump 180 may include a turbo pump (e.g., a constant speed or a
variable speed turbo pump), a dry pump (e.g., a constant speed or a
variable speed dry scroll pump or a constant speed or a variable
speed dry screw pump), or other pump capable of operating at vacuum
pressures greater than 3 Torr and less than 100 Torr (i.e., greater
than 400.0 Pa and less than 13,332.2 Pa). A second valve 182 may be
located between pump 180 and intersect point 165. First valve 172
and second valve 182 may regulate the flow and/or portion of
effluent gases 164 within exit path 177 and recirculation path 179.
Pump 180 may comprise an in-line exit port or a 90 degree exit
port. Pump 180 may comprise blades made from stainless steel, CMC
or other high strength, high temperature alloys or composites. In
various embodiments, a second pump 184 may be located downstream of
pump 180 and second valve 182. Second pump 184 may include a turbo
pump, a dry pump, or other suitable pump. In various embodiments,
second pump 184 may comprise a diaphragm pump.
[0096] Pump 180 and/or second pump 184 may be turned on and second
valve 182 may be opened to direct at least a portion of effluent
gases 164 into recirculation path 179. At least a portion of gas
effluent gases 164 within recirculation path 179 may be input into
reaction zone 130, thereby increasing the number of moles of carbon
passing through reaction zone 130 and available for reaction with
porous substrate 132. In various embodiments, a volume flow meter
196 may be in operable communication with first valve 172, second
valve 182, and/or a valve 190a to control the flow effluent gases
164 entering recirculation path 179. Stated differently, volume
flow meter 196 may be in operable communication with first valve
172, second valve 182, and/or valve 190a to control the flow
effluent gases 164 entering reaction zone 130. In various
embodiments, prior to being input into reaction zone 130, the
virgin gas and the recirculated gas may be combined in a single
conduit (as shown in FIG. 1). In various embodiments, the virgin
gas and the recirculated gas may be input into reaction zone 130
via separate conduits. Stated differently, a first conduit (e.g.
conduit 142) may be coupled between virgin gas source 140 and inlet
152, and a second conduit (e.g., conduit 163b), discrete from the
first conduit, may be coupled between valve 190a and inlet 152.
[0097] In various embodiments, additional valves 190 may be located
along exit path 177 and/or recirculation path 179. Valves 190 may
be configured to regulate a flow of effluent gas 164 through system
200. Valves 190, in combination with roughing pump 160 and/or pump
180, may also aid in maintaining the desired pressure level within
system 200. Opening or closing one or more valves 190 and/or
adjusting a speed of roughing pump 160 and/or pump 180 may control
the flow rate of effluent gas 164 through exit path 177 and
recirculation path 179. One or more pressure or other type sensor
192 may be located throughout system 200. Valves 190 may be opened
or closed and the speed of roughing pump 160 and/or pump 180 may be
adjusted in response to data output from sensors 192.
[0098] In various embodiments, one or more plasma conduits 202 may
be located between effluent gas outlet 162 and second valve 182 and
between second valve 182 and a trap 204. Plasma conduits 202 may
breakdown longer hydrocarbon chains. In various embodiments, plasma
conduits 202 may breakdown a hydrocarbon molecules containing six
or more carbon atoms into two or more hydrocarbon molecules
containing less than six carbon atoms. For example, plasma conduits
202 may breakdown a hydrocarbon molecule containing six carbon
atoms into two hydrocarbon molecules each containing three carbon
atoms, or into one hydrocarbon molecule containing four carbon
atoms and one hydrocarbon molecule containing two carbon atoms, or
into three hydrocarbon molecules each containing two carbon atoms.
A frequency of the plasma conduits maybe selected to breakdown a
particular molecule size. In various embodiments, the frequency of
the plasma conduits 202 may be selected to breakdown hydrocarbon
molecules containing six or more carbon atoms. In various the
frequency of the plasma conduits may be selected to breakdown
hydrocarbon molecules containing five or more carbon atoms. In
various embodiments, additional plasma conduits may be located
downstream of trap 204.
[0099] In various embodiments, trap 204 may be located downstream
from second valve 182. Trap 204 may comprise a one more sets of
spinning blades. The rotating blades may be configured to condense
hydrocarbons having six or more carbon atoms. In various
embodiments, heavier hydrocarbon (e.g., hydrocarbons comprised of
six or more carbon atoms) may condense in trap 204, thereby leaving
smaller hydrocarbon molecules in the gaseous state. Stated
differently, the effluent gas output from trap 204 may comprise
primarily smaller hydrocarbons (e.g., hydrocarbons comprised of
fewer than six carbon atoms).
[0100] In various embodiments, a hydrogen extraction component 206
may be disposed along recirculation path 179. Hydrogen extraction
component 206 may be configured to separate hydrogen gas from the
effluent gas. In various embodiments, hydrogen extraction component
206 comprises a PSA unit and/or magnetite filter configured to
remove hydrogen from the effluent gas. The extracted hydrogen may
exit recirculation path 179 via a conduit 208. Removal of excess
hydrogen may increase efficiency and densification rates as
hydrogen may tend to inhibit carbon deposition (i.e., densification
of porous substrate 132) in reaction zone 130.
[0101] In various embodiments, an electric arc variable frequency
or fixed DC corona plasma 210 may be implemented at the Venturi
point at outlet 162 (Le., proximate to retort lid 131). The
electric arc variable frequency or fixed DC corona plasma may
facilitate condensation of heavy hydrocarbons, which may lead to
formation of lighter hydrocarbon reaction gases within the effluent
gas 164 flowing through recirculation path 179 and into reaction
zone 130.
[0102] In system 200, the effluent gases 164 output from reaction
zone 130, may be kept at a pressure below atmospheric (e.g., less
than 760 Torr (101,325.0 Pa)), as the conduits 163 form a
semi-closed loop. In various embodiments, the effluent gases 164
may be recirculated through a condensing/plasma/"whipper" system to
remove condensable hydrocarbons of C5 variation or larger (i.e.,
hydrocarbons comprising 5 or more carbon atoms). The recirculated
effluent gases 164 may then be input into the reaction zone 130. In
this regard, the recirculated effluent gases 164 remain within the
system 200 plumbing such that a pressure throughout the system 200
remains fairly constant (e.g., the pressure remains under 100 Torr
(13,332.2 Pa)). The closed system may allow for increased efficacy
and lower energy costs as compared to conventional recirculation
systems, wherein the effluent gases are removed from the system
plumbing, filtered, and re-pressurized in an external tank before
being added back into the higher pressure input stream.
[0103] Recirculating effluent gases 164 may increase the number of
moles of small carbon molecules (e.g., molecules having five or
less carbon atoms or, for example, molecules having four or less
carbon atoms) flowing through the reaction zone 130 and available
for deposition within the porous substrate 132, without increasing
the flow and/or amount of virgin reaction gas input into the
system. Stated differently, recirculating effluent gas 164 may
increase deposition/densification rates, as more molecules are
passing through the reaction zone 130, which increases the number
of molecules that will make collisions (i.e., bond) with the porous
substrate 132. Accordingly, the disclosed system and method of
CVI/CVD may allow for faster densification of carbon fiber preforms
and/or densification to greater than 1.7 g/cc. The disclosed system
and method may also alleviate a need to machine porous substrate
132 to reopen closed surface pores. In this regard, system 200 may
allow the densification of porous substrate 132 to be completed in
a single CVI/CVD cycle.
[0104] With reference to FIG. 3, a system 300 for chemical vapor
infiltration and densification comprising a recirculation path with
cryogenic cooling stage is illustrated, in accordance with various
embodiments. System 300 may comprise a reaction chamber 329
comprising a retort 319 that defines a reaction zone 330. Stated
differently, reaction zone 330 is located in the interior of retort
319. Retort 319 may be similar to retort 19 in FIG. 6A. Retort 319
may comprise a retort lid 331, similar to retort lid 31 in FIG. 6B.
Retort lid 331 may be configured to have a Venturi effect. In
various embodiments, retort lid 331 may comprise a Venturi cone.
Stated differently, retort lid 331 may comprise a generally
frustoconical shape. Retort lid 331 may be located proximate an
outlet 362 of reaction zone 330.
[0105] A stage 316 may be located within reaction zone 330 and may
support one or more porous substrates 332, during the CVI/CVD
process. Virgin gas may be input, from virgin gas source 340, into
reaction zone 330 via an inlet 352 of reaction chamber 329. An MFC
346 may be in operable communication with virgin gas source 340 and
may measure and control a flow rate of virgin reaction gas input
into reaction zone 330. One or more inert gas inlets 354 may be in
fluidly coupled to reaction zone 330. Inert gas may be input into
reaction zone 330 to force atmospheric gases from reaction zone
330. Effluent gas 364 may exit reaction zone 330 via the outlet 362
located at retort lid 331. Upon exiting outlet 362, effluent gas
364 may be directed through a series of conduits (e.g., pipes) 363.
In various embodiments, an electric arc variable frequency or fixed
DC corona plasma 310 may be employed downstream of exhaust outlet
362.
[0106] In various embodiments, one or more plasma conduits 402 may
be located between outlet 362 and a trap 404. In various
embodiments, trap 404 may comprise a "whipper" having one or more
sets of rotating blades configured to breakdown (i.e., condense)
larger hydrocarbons. For example, a temperature within trap 404 may
cause hydrocarbon molecules comprising six or more carbon atoms to
condense.
[0107] System 300 may comprise a cryogenic-cooler 410. In various
embodiments, cryogenic cooler 410 may be a helium (He) cryogenic
cooler or a liquid nitrogen condenser. Cryogenic-cooler 410 may be
employed to condense (i.e., liquefy) lighter hydrocarbon gases
(e.g., hydrocarbons gases comprising hydrocarbon molecules having
six or less carbon atoms, or, for example, hydrocarbon gases
comprising hydrocarbon molecules having five or less carbon atoms).
Condensing hydrocarbon gases may allow hydrogen, which remains in a
gaseous state, to be readily extracted from cryogenic cooler 410.
In this regard, cryogenic-cooler 410 may comprise a hydrogen
extraction component. A frustoconical shaped conduit 408 may couple
trap 404 and cryogenic-cooler 410. The frustoconical shape of
conduit 408 may facilitate a Venturi effect. The gaseous hydrogen
may exit cryogenic-cooler 410 along exit path 377 (i.e., indicated
by arrows 381). The liquefied hydrocarbons may accumulate in a
conduit 414. A frustoconical shaped conduit 412 may be located at
the exhaust outlet of cryogenic cooler 410 and may be fluidly
coupled to cryogenic-cooler 410 and conduit 414. The frustoconical
shape of conduit 412 may allow for expansion of the hydrocarbons
exiting cryogenic-cooler 410 and may facilitate a phase change of
the hydrocarbons from the liquid state to the a gaseous state. Once
most or all the hydrogen is removed, the liquefied hydrocarbons may
be heated within conduit 414. The heating returns the small
hydrocarbons to a gaseous state.
[0108] A valve 384 may be opened and one or more pumps (e.g., a
primary pump 380 and one or more secondary pumps 382) located along
recirculation path 379 may be turned on such that the gaseous
hydrocarbons will flow from conduit 414 through recirculation path
379 (indicated by arrows 474). The flow of the effluent gas 364
through recirculation path 379 may be controlled via valve 384,
primary pump 380, and/or one or more secondary pumps 382. In
various embodiments, a volume flow meter 396 may be in operable
communication with a valve 390a (e.g., a one way flow valve) to
control the flow of recirculated gas entering reaction zone
330.
[0109] The flow of effluent gas 364 and the hydrogen gas extracted
in cryogenic cooler 410 may be controlled via a valve 372, a
throttle vale 376, a roughing pump 360, and/or a turbo pump 373. In
various embodiments, a portion 397 of the effluent gas output from
roughing pump 360 may be recirculated back into reaction zone 330.
A compressor pump 399 may be located downstream of roughing pump
360. In various embodiments, compressor pump 399 may comprise a
second cryogenic-cooler, PSA, magnetite filter, or other hydrogen
extraction component.
[0110] The vacuum pressure within reaction zone 330 and system 300
may be maintained at the desired level by opening and closing
throttle valve 376, valve 372, and/or valve 384 and by increasing
and decreasing the speed of roughing pump 360 and/or pump 380. In
various embodiments, additional valves 390 may be located along the
exit path 377 and/or recirculation path 379. One or more pressure
or other type sensor 392 may be located throughout system 300.
Valves 390 may be configured to regulate flow of effluent gas 364
through system 300. Opening or closing one or more valve 390 may
control the flow rate of effluent gas 364 through exit path 377
and/or recirculation path 379. Opening or closing one or more
valves 390 may also help maintain the desired pressure level within
system 300.
[0111] FIG. 4 is a graph 500 comparing the weight gain (i.e.,
densification) of a porous substrate sample 5 within a CVI/CVD
system employing recirculated effluent gas (line 502), as disclosed
herein, to the weight gain of a porous substrate sample 8 within a
CVI/CVD system employing an increased virgin gas flow rate (line
504), to the weight gain of a porous substrate sample 6 within a
control CVI/CVD system (line 506). Graph 500 illustrates that at 25
hours, an increased virgin gas flow rate increased the weight gain
of the porous substrate, as compared to the weight gain of the
control substrate, by approximately 4%. Whereas, at 25 hours
recirculating effluent gas increased the weight gain of the sample
substrate, as compared to the weight gain of the control substrate,
by approximately 37%. Graph 500 illustrates that a higher
efficiency and a more rapid densification may be achieved by
recirculating effluent gas as compared to increasing the virgin gas
flow. Accordingly, the disclosed systems and methods of CVI/CVD may
allow for faster densification of a carbon fiber preform and/or
densification to greater than 1.7 g/cc. The disclosed systems and
methods of CVI/CVD may allow for densification of a carbon fiber
preform without machining steps to re-open closed surface pores. In
this regard, the carbon fiber preform may be densified during a
single CVI/CVD cycle.
[0112] Referring to FIG. 5A, a method 600 of CVI/CVD is illustrated
in accordance with various embodiments. Method 600 may comprise
disposing a porous substrate within a reaction chamber (step 602),
establishing a sub-atmospheric pressure within the reaction chamber
(step 604), introducing a hydrocarbon reaction gas into a reaction
zone of the reaction chamber to densify the porous substrate (step
606), and withdrawing unreacted hydrocarbon reaction gas from the
reaction chamber (step 608). In various embodiments, the unreacted
hydrocarbon reaction may comprise hydrocarbon molecules having six
or more carbon atoms. Method 600 may further comprise removing at
least a portion of the hydrocarbon molecules having six or more
carbon molecules from the unreacted hydrocarbon reaction gas by
causing the portion of the hydrocarbon molecules having six or more
carbon atoms to condense (step 610). In various embodiment, step
610 may comprise flowing the unreacted hydrocarbon reaction gas
through a trap including one or more sets of rotating blades.
Method 600 may further comprise recirculating at least a portion of
the unreacted hydrocarbon reaction gas back into the reaction zone
(step 612).
[0113] Referring to FIG. 5B, a method 620 of CVI/CVD is illustrated
in accordance with various embodiments. Method 620 may comprise
disposing a porous substrate within a reaction chamber (step 622),
applying an electrical voltage to the porous substrate (step 624),
and establishing a sub-atmospheric pressure within the reaction
chamber (step 626). In various embodiments, step 626 may comprise
inputting inert gas into the reaction chamber.
[0114] Method 620 may further comprise introducing a hydrocarbon
reaction gas into a reaction zone of the reaction chamber to
densify the porous substrate (step 628), and withdrawing unreacted
hydrocarbon reaction gas from the reaction chamber (step 630). In
various embodiments, the unreacted hydrocarbon reaction may
comprise hydrocarbon molecules having six or more carbon atoms.
Method 620 may further comprise removing at least a portion of the
hydrocarbon molecules having six or more carbon molecules from the
unreacted hydrocarbon reaction gas (step 632). In various
embodiment, step 632 may comprise flowing the unreacted hydrocarbon
reaction gas through a trap including one or more sets of rotating
blades. In various embodiment, step 632 may comprise applying an
electric arc to the unreacted hydrocarbon reaction gas withdrawn
from the reaction chamber.
[0115] Method 620 may further comprise extracting hydrogen from the
unreacted hydrocarbon reaction gas (step 634). In various
embodiment, step 634 may comprise flowing the unreacted hydrocarbon
reaction gas through at least one of a cryogenic-cooler or a
pressure swing absorption unit. Method 620 may further comprise
recirculating at least a portion of the unreacted hydrocarbon
reaction gas back into the reaction zone (step 636), and heating at
least one of the hydrocarbon reaction gas or the portion of the
unreacted hydrocarbon reaction gas recirculated into the reaction
zone using a charged coil located proximate an inlet of the
reaction chamber (step 638). In various embodiments, the charged
coil may provide an electrical conduction path to either charge or
ground an interior wall of the reaction chamber.
[0116] Benefits, other advantages, and solutions to problems have
been described herein with regard to specific embodiments.
Furthermore, the connecting lines shown in the various figures
contained herein are intended to represent exemplary functional
relationships and/or physical couplings between the various
elements. It should be noted that many alternative or additional
functional relationships or physical connections may be present in
a practical system. However, the benefits, advantages, solutions to
problems, and any elements that may cause any benefit, advantage,
or solution to occur or become more pronounced are not to be
construed as critical, required, or essential features or elements
of the disclosure.
[0117] The scope of the disclosure is accordingly to be limited by
nothing other than the appended claims, in which reference to an
element in the singular is not intended to mean "one and only one"
unless explicitly so stated, but rather "one or more." It is to be
understood that unless specifically stated otherwise, references to
"a," "an," and/or "the" may include one or more than one and that
reference to an item in the singular may also include the item in
the plural. All ranges and ratio limits disclosed herein may be
combined.
[0118] Moreover, where a phrase similar to "at least one of A, B,
and C" is used in the claims, it is intended that the phrase be
interpreted to mean that A alone may be present in an embodiment, B
alone may be present in an embodiment, C alone may be present in an
embodiment, or that any combination of the elements A, B and C may
be present in a single embodiment; for example, A and B, A and C, B
and C, or A and B and C. Different cross-hatching is used
throughout the figures to denote different parts but not
necessarily to denote the same or different materials.
[0119] The steps recited in any of the method or process
descriptions may be executed in any order and are not necessarily
limited to the order presented. Furthermore, any reference to
singular includes plural embodiments, and any reference to more
than one component or step may include a singular embodiment or
step. Elements and steps in the figures are illustrated for
simplicity and clarity and have not necessarily been rendered
according to any particular sequence. For example, steps that may
be performed concurrently or in different order are illustrated in
the figures to help to improve understanding of embodiments of the
present disclosure.
[0120] Any reference to attached, fixed, connected or the like may
include permanent, removable, temporary, partial, full and/or any
other possible attachment option. Additionally, any reference to
without contact (or similar phrases) may also include reduced
contact or minimal contact. Surface shading lines may be used
throughout the figures to denote different parts or areas but not
necessarily to denote the same or different materials. In some
cases, reference coordinates may be specific to each figure.
[0121] Systems, methods and apparatus are provided herein. In the
detailed description herein, references to "one embodiment," "an
embodiment," "various embodiments," etc., indicate that the
embodiment described may include a particular feature, structure,
or characteristic, but every embodiment may not necessarily include
the particular feature, structure, or characteristic. Moreover,
such phrases are not necessarily referring to the same embodiment.
Further, when a particular feature, structure, or characteristic is
described in connection with an embodiment, it is submitted that it
is within the knowledge of one skilled in the art to affect such
feature, structure, or characteristic in connection with other
embodiments whether or not explicitly described. After reading the
description, it will be apparent to one skilled in the relevant
art(s) how to implement the disclosure in alternative
embodiments.
[0122] Furthermore, no element, component, or method step in the
present disclosure is intended to be dedicated to the public
regardless of whether the element, component, or method step is
explicitly recited in the claims. No claim element is intended to
invoke 35 U.S.C. 112(f) unless the element is expressly recited
using the phrase "means for." As used herein, the terms
"comprises," "comprising," or any other variation thereof, are
intended to cover a non-exclusive inclusion, such that a process,
method, article, or apparatus that comprises a list of elements
does not include only those elements but may include other elements
not expressly listed or inherent to such process, method, article,
or apparatus.
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